1. Technical Field
The present invention relates to a technique of inspecting a surface state of an object.
2. Related Art
There is well known a technique of inspecting the surface state of the object by analyzing an image obtained with a camera or an image sensor. This is generally called appearance inspection. For example, the appearance inspection is utilized to detect surface defects of magnetic and optical disks, a copper-clad laminate, a silicon wafer, a steel plate and a steel sphere, and a molded product.
For example, in a technique proposed in Japanese Unexamined Patent Publication No. 5-322543, a flat-plate surface light source irradiates an object surface with inspection light having a lightness gradient, and a portion whose lightness gradient is different from that of its surrounding portion in an image is determined as a defect. In a technique proposed in Japanese Unexamined Patent Publication No. 2009-97977, four pieces of lighting disposed in different directions are sequentially lit to take four images, and existence or nonexistence of a flaw or irregularity is discriminated from an image obtained by computing exclusive OR of the four images. In a technique proposed in Japanese Patent No. 3634985, the object is irradiated with measuring light such that a focal line is generated in the object surface, a change in intensity of reflected light is observed in the object surface while the object is vertically moved, thereby measuring the depth of the flaw.